Multiple visual pathways reach the thalamus and cortex in mammals, including primates, and a large set of cortical visual areas together comprise a sizable fraction of the neocortical mantle. In the proposed research we intend to use neuroanatomical tracer methods, histochemistry including immunohistochemistry, ligand binding and lesion techniques in order to achieve four goals. First we propose to determine the main patterns of connectivity of the striate and extrastriate cortical area using the cat as a "model preparation" because of the ease of identifying connectionally distinct extrageniculate thalamic subdivisions by acetylcholinesterase histochemistry and the consequent ease of referring the connections found to know organizations of thalamo-corticothalamic connections. The second goal of the proposed work is to determine whether the cholinesterase activity patterns in the extrageniculate and geniculate thalamic nuclei are indicative of cholinergic pathways, using ligand binding and immunohistochemical methods and lesions and, with the collaboration of Dr. Roffler-Tarlov, biochemical assays of choline acetyltransferase and acetylcholinesterase activity. The third goal is to explore the distribution of cholinesterases in the geniculostriate and extrageniculostriate visual system of Macaque monkeys following on our preliminary observation of discrete laminar and compartmental localization of these enzymes in the lateral geniculate body, striate cortex, pulvinar and extrastriate cortex. We propose to determine further whether these histochemically distinct compartments can be seen in human autopsy specimens of thalamus and cortex, which would provide a natural and direct bridge between the proposed experimental work and work on human brains in health and disease.